Gas Chromatography — mass spectrometry

Gas chromatography-mass spectrometry benchtop system. (Courtesy of Agilent Technologies.) 

The nitrogen rule tells you whether you have an even or an odd formula weight compound. 

Resolution tells you how accurately you can differentiate two masses. Unit resolution tells you that you can differentiate one mass difference. 

In mass spectrometry, the resolving power, that is, the ability to differentiate two masses, is given by the resolution R, defined as the nominal mass divided by the difference between two masses that can be separated  

The mass difference is usually measured at the mean of some fixed fraction of the peak heights, for example, at 10%. A resolution of 1000 means that a molecule of miz = 1000 would be resolved from miz = 1001 (or miz = 10.00 from 10.01) or miz = 500.0 is resolved from miz — 500.5. 

Gas Chromatography-Mass Spectrometry (g.c.-m.s.).—Syntheses of twenty different steroids (oestrogens, androgens, progesterone, and corticosteroids and their metabolites) with from two to four deuterium atoms per molecule have 

Turecek and L. Kohout, Collect. Czech. Chem. Commun., 1980, 45, 2433. 

6 High-performance Liquid Chromatography (h.p.l.c.) and other Chromatographic Methods 

A review of h.p.l.c. of steroid hormones traces the history of the subject, and describes methods for h.p.l.c. analyses of the main classes of steroids in biological fluids and pharmaceuticals.112 

An extensive review (155 references) of the separation and determination of D vitamins by h.p.l.c. includes discussion of the problem of instability, and a detailed 

The time has long since passed when one could rely on gas chromatographic or liquid chromatographic data alone to identify unknown compounds in water or other environmental samples. The sheer numbers of compounds present in such materials would invalidate the use of these tedmiques, and even in the case of simple mixtures the time required for identification would be too great to provide essential information in the case, for example, of accidental spillage of an oiganic substance into a water course or inlet to a water treatment plant where information is required very rapidly. 

Finnigan MAT are one of the major suppliers of this equipment. They supply equipment for single stage quadruple mass spectrometry, mass spectrometry-mass spectrometry, high mass high resolution mass spectrometry, ion trap detection, and gas chromatography-mass spectrometry. 

0WA-20I30B organic in water gas chromatograph mass spectrometer (Finnigan MAT) 

This system combines hardware and software features not foimd in any 

As an example of the application of gas chromatography-mass spectrometry. Fig. 1.6 shows a reconstructed ion chromatograph obtained for an industrial waste sample. The Finnigan MAT 1020 instrument was used in this work. Of the 27 compoimds searched for, 15 were found. These data were automatically quantified. This portion of the report contains the date and time at which the run was made, the sample description, who submitted the sample to the analyst, followed by the names of the compounds. If no match for a library entry weis found, the component was listed not foimd. Also shown is the method of quantification and the area of the peak (height could also have been chosen). 

A gas chromatography-mass spectrometry system is used to measure concentrations of target volatile and semivolatile petroleum constituents. It is not typically used to measure the amount of total petroleum hydrocarbons. The advantage the technique is the high selectivity, or ability to confirm compound identity through retention time and unique spectral pattern. 

The current method (EPA SW-846 8260) for the analysis of volatile compounds reveals that most of the compounds listed in these methods are not 

At the present time, gas chromatography-mass spectrometry (GC-MS) is the most versatile analytical technique for the solution of this problem. In an on-line operation each component separated and eluted from the gas chromatograph can be individually scanned by the mass spectrometer (MS) to give a mass spectrum which will definitely identify the component by comparison with reference data. There are a number of potential advantages inherent in the combined use of GC and MS which are listed below, and these have been applied to the multicomponent analysis of many different compound classes. 

Not only can compounds be identified which are known and for which reference spectra are available, but it is often possible to determine the structure of previously unencountered compounds from interpretation of their spectra. Such interpretations are based on existing knowledge of the relationship between structure and modes of fragmentation and rearrangement of molecules which take place in the ion source of the mass spectrometer. If the spectrum suggests a possible structure, this can be checked directly by comparison with the mass spectrum of synthesized authentic material. 

Good qualitative spectra of compounds can be obtained over a wide range of concentrations (approx. 10 ), even from very small sample components (low nanogram level). This permits identification of the majority of components in a single sample. 

Although GC is a good method for compound quantification, it is only semiquantitative at best when peaks are unresolved. Refined GC-MS methods are available which will overcome this difficulty. 

The great majority of today s GC-MS applications ntiUze one-dimensional capillary GC with quadrupole MS detection and electron ionization. Nevertheless, there are snbstantial numbers of applications using different types of mass spectrometers and ionization techniqnes. The proliferation of GC-MS applications is also a result of conunercially available easy-to-handle dedicated mass spectral libraries (e.g., NIST/EPA/NIH 2005 WILEY Registry 2006 MassFinder 2007 and diverse printed versions such as Jennings and Shibamoto, 1980 Joulain and Konig, 1998 and Adams, 1989, 1995, 2007 inclusive of retention indices) providing identification of the separated componnds. However, this type of identification has the potential of prodndng some unreliable resnlts, if no additional information is used, since some compounds, for example, the sesquiterpene 

FIGURE 2.6 GC-EIMS-MS ofkhusimone of vetiver oil. (From Cazaussus, A., etal., 1988. Chromatographia, 25 865-869. With permission.) 

2 High-Resolution Gas Chromatography-Fourier Transform Infrared Spectroscopy 

In the latter publication, for example, the vapor-phase IR spectra of all the four isomers of pulegol and dihydrocarveol are shown, which have been extracted from a GC/FTIR run. These examples convincingly demonstrate the capability of distinguishing geometrical isomers with the aid of vapor-phase IR spectra, which cannot be achieved by their mass spectra. A broad application of GC-FTIR in the analysis of essential oils, however, is limited by the lack of sufficient vapor-phase spectra of uncommon compounds, which are needed for reference use, since the spectra of isolated molecules in the vapor phase can be significantly different from the corresponding condensed-phase spectra. 

Comparing GC/FTIR and GC/MS, advantages and limitations of each technique become visible. The strength of IR lies—as discussed before—in distinguishing isomers, whereas identification of homologues can only be performed successfully by MS. The logical and most sophisticated way to overcome these limitations has been the development of a combined GC/FTIR/MS instrument, whereby simultaneously IR and mass spectra can be obtained. 

Our personal experience with gas chromatographic-mass spectrometric analysis of bile acids is limited to the use of a modified Atlas CH-4 mass spectrometer connected to the gas chromatography column via a molecule separator of the jet type (8, 16), and to the use of prototypes and production models of the LKB 9000 instrument. 

When the conditions of analysis are chosen, the requirements of both the gas chromatographic and the mass spectrometric parts must be considered. The combination instrument differs from a conventional gas chromatograph since there is a vacuum at the exit of the column. The gas flow rate must be chosen so that the pressure in the column does not get too low. If this happens peak distortion and loss of resolution occurs. Flow rates of 30-60 ml/min are suitable when a two-stage jet separator is used with helium as carrier gas, and when the columns, 3-4 mm i.d., are packed with 80-100 or 100-120 mesh packing. Under these conditions 99-99.5% of the helium is removed in the separator and about 60-70% of the sample reaches the ion source (16). The pressure in the analyzer tube is about 1-3 x 10 mm Hg. 

Some workers use a splitter before the mass spectrometer inlet to be able to attach other detection or collection devices. In routine analyses part of the total ion current produced in the mass spectrometer is used to follow the appearance of organic material from the column. A gas chromatographic analysis should, however, always be made prior to the analysis in the combination instrument to avoid introduction of grossly contaminated samples. 

When a direct inlet system is used, spectra can be obtained of the free bile acids. This is not possible with a gas chromatographic inlet. The simplest derivative which can be analyzed with the combination instrument is the methyl ester. Valuable information on the nature of the fragment ions can be obtained by analysis of both the methyl and ethyl esters. Particularly for gas chromatographic reasons it is better, however, to protect hydroxyl groups by acetylation, trifluoroacetylation, or trimethylsilylation. 

The choice of bile acid derivative depends on the nature and complexity of the bile acid mixture to be analyzed. Derivative formation is described in the chapter on gas chromatography. Generally it is of advantage to use 

Virtually all volatile aromatic and flavorsome lipid-derived compounds are analyzed using gas chromatography-mass spectrometry (GC-MS). The components of interest are isolated initially, concentrated, then injected onto a suitable capillary column and detected using a mass spectrometer. 

The principle of GC-MS involves the bombardment of organic molecules of interest in the vapor phase with electrons to form positively charged ions, which fragment in a number of different ways to give smaller ionized entities. These ions are propelled through magnetic or electrostatic fields and 

Isolation and Concentration of Volatile Lipid-Derived Components 

Numerous techniques have been developed to isolate and concentrate aroma compounds derived from lipids or other components, from other constituents than dairy foods. The most widely used methods are based on volatility and/or solubility. 

Distillation techniques, such as steam distillation, are typically carried out in a rotary evaporator after the sample has been solubilized in an organic solvent. The distillate is injected directly onto a suitable GC column. This method is used widely due to its simplicity and because components with high boiling points are recovered easily. High-vacuum distillation is used widely to isolate volatile components from solvent extracts. This procedure often requires an extraction step to remove water. 

The most precise procedure for detection of banned substances is a combination of GC and MS. Gas chromatography/mass spectrometry is a two-step process, where GC separates the sample 

When measured to four decimal places, the mass of these compounds are in fact diflFerent, and this difference is detectable. In a high-resolution mass spectrometer, the molecular ion for the first compound will appear near mlz= 84.0573, while the molecular ion of the second compound will appear near mlz= 84.0936. In this way, the molecular formula of an unknown compound can be determined via high-resolution mass spectrometry. The mass of the molecular ion is measured accurately, and a simple computer program can then calculate the correct molecular formula. The computer program is not entirely necessary, because published data tables can be cross-referenced to find the matching molecular formula. 

29 How would you distinguish between each pair of compounds using high-resolution mass spectrometry OH 

An example of a chromatogram, showing five different compounds, each with a unique retention time. 

Characterization of various types of damage to DNA by oxygen-derived species can be achieved by the technique of gas chromatography-mass spectrometry (GC-MS), which may be applied to DNA itself or to DNA-protein complexes such as chromatin (Dizdaroglu, 1991). For GC-MS, the DNA or chromatin is hydrolysed (usually by heating with formic acid) and the products are converted to volatile derivatives, which are separated by gas chromatography and conclusively identified by the structural evidence provided by a mass spectrometer. Stable isotope-labelled bases may be used as internal standards 

A very useful innovation in sample introduction systems is the use of a gas chromatograph coupled to a mass spectrometer. In effect, the mass spectrometer acts in the role of detector. In this technique, known as gas chromatography-mass spectrometry (GC-MS), the gas stream emerging from the gas chromatograph is admitted through a valve into a tube, where it passes over a molecular leak. Some of the gas stream is thus admitted into the ionization chamber of the mass spectrometer. In this way it is possible to obtain the mass spectrum of every component in a mixture being injected into the gas chromatograph. 

A drawback of this method involves the need for rapid scanning by the mass spectrometer. The instrument must determine the mass spectrum of each component in the mixture before the next component exits from the gas chromatography column, in order that one substance is not contaminated by the next fraction before its spectrum has been obtained. 

Since high-efficiency capillary columns are used in the gas chromatograph, in most cases compounds are completely separated before the gas stream is analyzed. The instrument must have the capability of obtaining at least one scan per second in the range of 10 to 300 amu. Even more scans are necessary if a narrower range of masses is to be analyzed. 

The effluent from the gas-chromatograph part of the instrument can also be directed into an FT-IR instrument so that infrared spectra rather than mass spectra can be obtained. In that case, the infrared spectrophotometer acts as the detector for the gas chromatograph. 

With a GC-MS system, one can also analyze a mixture and conduct a library search on each component of the mixture. If the components are known compounds, they can be identified tentatively by 

Polymers contain trace ammmts of residues of the organic catalyst used in their preparation and the identification of these is often necessary. The use of gas chromatography is conjunction with mass spectrometry is required in order to separate the complex mixture of components that are extracted. For example, tetra-methylsuccinodinitrile has been detected in extracts of polymers prepared using azobisiso-butyronitrile catalyst. Substantial losses of tetramethylsuccinodinitrile occur in the evaporation of methanolic solutions which explained earlier difficulties in detecting residues of this catalyst. Even without concentration of the polymer extract it was possible to achieve a lower limit of detection of 20 ppm in the polymer. 

A further family of catalysts often used are peroxides (eg. benzoyl or lauroyl peroxide), these produce acids as residues which may be detected by mass spectrometry or by methylation of the evaporated extract prior to gas chromatography - mass spectrometry examination. 

The analyst in the plastics industry may be required to trace the cause of odour and taint produced in foodstuffs packaged in plastic materials. This provides good examples of the use of high sensitivity gas chromatography - mass spectrometry in the identification of such compoimds. Two methods have proved useful for the concentration of these components. 

We are using GC/MS for profiling primary metabolites in M. truncatula. This approach allows for the simultaneous profiling of approximately 300 to 500 components, including amino acids, organic acids, monosaccharides, disaccharides, 

A large number of primary metabolites can be readily identified because most of these compounds are commercially available. Standard compounds are derivatized, co-chromatographed, and the data are deposited into databases. Unknown metabolites are identified by matching chromatographic retention times 

Deconvolution and Identification Software (AMDIS) provided with many Hewlett 

Packard GC/MS instruments. We exploit both custom and commercial libraries for metabolite identifications. By using this approach we have identified a large number (-130 currently) of primary metabolites in M. truncatula (Fig.3.4). This method has also been used to compare the profiles of various M. truncatula tissues (data not shown). 

The primary limitation associated with GC/MS is the need for derivatization. Derivatization introduces additional complexity to the system and is not 100% efficient. Inefficient reactions result in the presence of multiple derivatized forms of the same compound. For example, we can detect three different derivatization products of the amino acid asparagine (mw = 132) in M. truncatula roots (Fig.3.4). These include asparagine, N,0-TMS (mw = 276), asparagine, N,N,0-TMS (mw = 348), and asparagine, N,N,N,0-TMS (mw = 420). Inefficiency of the derivation reactions also limits the lower concentration range of analytes that can be profiled. Finally, derivatization is not capable of achieving volatility for all compounds, such as many of the flavonoid glycosides. If derivatization is successful and the analyte is 

Trace Analysis Unit, Bernhard Baron Memorial Research Laboratories 339 Goldhawk Road, London 

Edited by K. Blau and J. M. Halket 1993 John Wiley Sons Ltd 

In addition to the usual advantages for chromatography, including reduction in polarity, protection of labile compounds, alteration of retention times and resolution and enhancement of sensitivity, there are further advantages to be gained from the use of derivatives in GC-MS, and these are covered in the next section. 

Tbe reader new to mass spectrometry is advised to consult an appropriate introductory text [2-9]. A few mass spectrometric terms will be explained here by way of background and to outline the principles of choosing a lerivative. As in the flame ionization detector, ions are produced in the mass spectrometric detector, but the mass spectrometer is able to analyze these ions further according to their molecular weights or rather, mass-to-charge ratios (m/z, see below) to provide a mass spectrum. Different principles are employed to achieve this in a variety of types of mass spectrometer. The instruments most commonly used in GC—MS are known as magnetic sector, quadrupole and ion trap mass spectrometers. Their differences are not further described here. Bench-top systems are of the quadrupole or ion trap type. 

The mass spectrometric mode of detection, therefore, has properties related to the actual structure of the analyte and not just the elemental composition. Since chemical derivatization can radically alter the analyte structure, it can have a profound and often advantageous effect on the specificity and sensitivity of detection. Several striking examples of this will be given. 

Handbook of Essential Oils Science, Technology, and Applications 

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Jaeger, H., Capillary Gas Chromatography Mass Spectrometry in Medicine and Pharmacology, Huetig, New York, 1987. 

McFadden, W.H., Techniques of Combined Gas Chromatography/Mass Spectrometry, Wiley, New York, 1973. McLafferty, F.W., Tandem Mass Spectrometry, Wiley, New York, 1983. 

A review pubHshed ia 1984 (79) discusses some of the methods employed for the determination of phenytoia ia biological fluids, including thermal methods, spectrophotometry, luminescence techniques, polarography, immunoassay, and chromatographic methods. More recent and sophisticated approaches iaclude positive and negative ion mass spectrometry (80), combiaed gas chromatography—mass spectrometry (81), and ftir immunoassay (82). 

Confirmation of the identities of nitrosamines generally is accompHshed by gas chromatography—mass spectrometry (gc/ms) (46,87). High resolution gc/ms, as well as gc/ms in various single-ion modes, can be used as specific detectors, especially when screening for particular nitrosamines (87) (see Analytical LffiTHODS Trace and residue analysis). 

The combined techniques of gas chromatography/mass spectrometry (gc/ms) are highly effective in identifying the composition of various gc peaks. The individual peaks enter a mass spectrometer in which they are analyzed for parent ion and fragmentation patterns, and the individual components of certain resoles are completely resolved. 

The possibiHties for multidimensional iastmmental techniques are endless, and many other candidate components for iaclusion as hyphenated methods are expected to surface as the technology of interfacing is resolved. In addition, ternary systems, such as gas chromatography-mass spectrometry-iafrared spectrometry (gc/ms/ir), are also commercially available. 

One of the reasons for lack offlterature was probably because environmental analysis depends heavily on gas chromatography/mass spectrometry, which is not suitable for most dyes because of their lack of volatility (254). However, significant progress is being made in analyzing nonvolatile dyes by newer mass spectral methods such as fast atom bombardment (EAB), desorption chemical ionization, thermospray ionization, etc. 

GAS CHROMATOGRAPHY/MASS SPECTROMETRY DETECTION OF XENOBIOTICS IN ENVIRONMENTAL... 

Identification of stmctures of toxic chemicals in environmental samples requires to use modern analytical methods, such as gas chromatography (GC) with element selective detectors (NPD, FPD, AED), capillary electrophoresis (CE) for screening purposes, gas chromatography/mass-spectrometry (GC/MS), gas chromatography / Fourier transform infra red spectrometry (GC/FTIR), nucleai magnetic resonance (NMR), etc. 

When the gas chromatograph is attached to a mass spectrometer, a very powerful analytical tool (gas chromatography-mass spectrometry, GC-MS) is produced. Vapour gas chromatography allows the analyses of mixtures but does not allow the definitive identification of unknown substances whereas mass spectrometry is good for the identification of a single compound but is less than ideal for the identification of mixtures of... 

F.W. Karasek and R.E. Clement, Basic Gas-Chromatography-mass spectrometry Principles and Techniques, Elsevier, Amsterdam, 1988. ISBN 0444427600. 

BS ISO 12884 Polycyclic aromatic hydrocarbons Collection of filters with gas chromatography/mass spectrometry... 

Deuterium exchange of conjugated enones and dienones on pretreated gas chromatography columns has been found useful for the characterization of these compounds by combined gas chromatography-mass spectrometry. ... 

In gas chromatography/mass spectrometry (GC/MS), the effluent from a gas chromatograph is passed into a mass spectrometer and a mass spectrum is taken every few milliseconds. Thus gas chromatography is used to separate a mixture, and mass spectrometry used to analyze it. GC/MS is a very powerful analytical technique. One of its more visible applications involves the testing of athletes for steroids, stimulants, and other performance-enhancing drugs. These drugs are converted in the body to derivatives called metabolites, which are then excreted in the... 

Phenyl-2//-triazolo[4,5-/]quinoline was prepared and used as optical bright-ener, light, and drug stabilizer (86GEP1), whereas 3,5,7-3//-trimethyl-triazolo[4, 5-/]quinoline was identified by gas chromatography/mass spectrometry as a water pollutant of the Shinano River (Japan) (82MI6). 

H. J. Goites, B. M. Bell, G. D. Pfeiffer and J. D. Graham, Multidimensional chromatography using on-line coupled microcolumn size exclusion cliromatography-capillary gas chromatography-mass spectrometry for determination of polymer additives , J. Microcolumn Sep. 1 278-288. (1989)... 

Figure 15.8 Multidimensional GC-MS separation of urinary acids after derivatization with methyl chloroformate (a) pre-column cliromatogram after splitless injection (h) Main-column selected ion monitoring cliromatogram (mass 84) of pyroglutamic acid methyl ester. Adapted from Journal of Chromatography, B 714, M. Heil et ai, Enantioselective multidimensional gas chromatography-mass spectrometry in the analysis of urinary organic acids , pp. 119-126, copyright 1998, with permission from Elsevier Science.

Gudzinowicz, B. J. and Gudzinowicz, M. J. Analysis of Drugs and Metabolites by Gas Chromatography Mass Spectrometry (Vols. 1-5). New York Marcel Dekker, 1977. 

Gas chromatography/mass spectrometry (GC/MS) is the synergistic combination of two powerful analytic techniques. The gas chromatograph separates the components of a mixture in time, and the mass spectrometer provides information that aids in the structural identification of each component. The gas chromatograph, the mass spectrometer, and the interface linking these two instruments are described in this chapter. 

Karasek, F. W., and Clement, R. E. Basic Gas Chromatography-Mass Spectrometry—Principles and Techniques. New York Elsevier, 1991. 

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